1. Field of the Invention
The present invention relates to a method of measuring a resonant frequency of a resonator, and more particularly to a method of measuring a resonant frequency of an individual resonator, a plurality of which constitute a filter.
2. Description of Related Art
A filter characteristic such as resonant frequency has to be adjusted after its manufacturing process is completed, because the characteristic usually deviates from its target due to various deviation factors such as dielectric constant of a substrate, thickness of layers, accuracy of a mask, manufacturing process conditions and the like. Such characteristic adjustment, or tuning is especially necessary for narrow band and low ripple filters.
Before or during such adjustment, it is necessary to accurately measure the resonant frequency of each resonator constituting a filter. Conventionally, a resonant frequency of each resonator is measured using a pair of probes attached to a resonator to be measured. Also, a coupling degree between two resonators selected arbitrarily among others is measured by the probes to check whether the coupling degree is realized as originally designed. However, the resonant frequency of an individual resonator and the coupling degree of two resonators cannot be accurately measured because of electromagnetic interference between the resonator to be measured and other neighboring resonators.